介词的基本用法与习惯搭配He came back late, ________ which time all the guests had already left
—Peter, hurry up! You ______ on the phone. —Oh, I ______. Thank you.
I can’t leave the office now. A lot of work ________ to be done.
This book _____ ten units, ______ three mainly revision.
When his mother came in, the boy pretended ______.
My younger brother dreams ___________ a spaceman.